Animals have been marked for identification purposes for hundreds, if not thousands, of years. Animals are marked for identification in a variety of applications. Some animals are used for research and it is important to track which animal was exposed to a given set of experimental conditions. Some animals are used for breeding stock and it is useful to track which animals pass on desirable and undesirable traits to their offspring. Some animals are kept as pets and it is useful to identify animal ownership, animal type, licensing or need for special care. Some animals are used in competition and it is useful to identify animals to reduce animal substitution or other unfair competitive practices.